Rosuvastatin calcium (monocalcium bis(+)7-[4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-methylsulfonylaminopyrimidin)-5-yl]-(3R,5S)-dihydroxy-(E)-6-heptenoate) is an HMG-CoA reductase inhibitor, developed by Shionogi for the once daily oral treatment of hyperlipidaemia (Ann Rep, Shionogi, 1996; Direct communications, Shionogi, 8 Feb. 1999 & 25 Feb. 2000). Rosuvastatin calcium is a superstatin, which can lower LDL-cholesterol and triglycerides more effectively than first generation drugs. Rosuvastatin calcium has the following chemical formula:

Rosuvastatin calcium is marketed under the name CRESTOR for treatment of a mammal such as a human. According to the maker of CRESTOR, it is administered in a daily dose of from about 5 mg to about 40 mg. For patients requiring less aggressive LDL-C reductions or who have pre-disposing factors for myopathy, a 5 mg dose is recommended, while 10 mg dose is recommended for the average patient, 20 mg dose for patients with marked hyper-cholesterolemia and aggressive lipid targets (>190 mg/dL), and the 40 mg dose for patients who have not been responsive to lower doses.
Rosuvastatin is an enantiomerically pure compound having two chiral centers at positions 3 and 5 of the molecule. Two of the four diastereoisomers of Rosuvastatin calcium are (3R,5R) and (3R,5S) derivatives. These diastereoisomers can be detected by reverse phase HPLC.
The synthetic process disclosed in US RE37,314E for rosuvastatin involves reduction of a keto-ester of a rosuvastatin at carbon 5 to obtain a diol ester. This reduction at position 5 is a standard typical step in the synthesis of statins. This reduction step however can result in diastereoisomeric impurities.
WO 2005/040134 discloses a process that is reported to reduce the diastereoisomer content of rosuvastatin through lactonization, or through conversion of amorphous rosuvastatin to crystalline rosuvastatin and subsequent conversion to the amorphous form.
There is a need in the art for preparation of diastereomerically pure rosuvastatin and its intermediates.